This invention is in the field of integrated circuits. Embodiments of this invention are more specifically directed to the integration of large capacitance value capacitors, serving as decoupling capacitors, into the integrated circuit itself.
Decoupling capacitors are a staple component in modern electronic systems. As fundamental in the art, the current demanded by digital and analog functions in the electronic systems vary over time, with some variations being relatively large and sudden. Non-ideal power supplies cannot respond instantaneously to large and rapid changes in current demand, causing variations in the power supply voltage. These power supply voltage variations appearing at integrated circuit functions in the system are considered as noise. Because the operation of modern high performance integrated circuits is vulnerable to power supply noise, external decoupling capacitors are commonly implemented in electronic systems, for example connected between the power supply and ground terminals at each integrated circuit, to absorb this power supply voltage noise caused by varying current demand.
As known in the art, the effectiveness of decoupling capacitors improves with the proximity of the capacitors to the integrated circuit. Not only does a closely-placed capacitor provide the best decoupling effect, but parasitic inductance of conductors between the capacitors and the integrated circuit functions is minimized, such inductance contributing to the undesired noise. Tradeoffs between decoupling effectiveness (i.e., large capacitance values, close proximity) and the component and manufacturing cost.
Many modern electronic devices and systems now include substantial computational capability for controlling and managing a wide range of functions and useful applications. Many of these electronic devices and systems are now portable or handheld devices. For example, many mobile devices with significant computational capability are now available in the market, including modern mobile telephone handsets such as those commonly referred to as “smartphones”, personal digital assistants (PDAs), mobile Internet devices, tablet-based personal computers, handheld scanners and data collectors, personal navigation devices, and the like. An important class of mobile devices are implantable medical devices, such as pacemakers, defibrillators, and the like. Many mobile devices, including implantable medical devices, now rely on solid-state memory not only for data storage during operation, but also as non-volatile memory for storing program instructions (e.g., firmware) and for storing the results and history of previous operations and calculations. Modern mobile devices typically include substantial non-volatile memory capacity, often amounting to as much as one or more gigabytes.
Ferroelectric random-access memory (FeRAM) is a popular non-volatile solid-state memory technology, particularly in implantable medical devices. A recently developed technology for realizing non-volatile solid-state memory devices involves the construction of capacitors in which the dielectric material is a polarizable ferroelectric material, such as lead zirconate titanate (PZT) or strontium-bismuth-tantalate (SBT). Hysteresis in the charge-vs.-voltage (Q-V) characteristic, based on the polarization state of the ferroelectric material, enables the non-volatile storage of binary states in those capacitors. In contrast, conventional MOS capacitors lose their stored charge on power-down of the device. It has been observed that ferroelectric capacitors can be constructed by processes that are largely compatible with modern CMOS integrated circuits, for example placing capacitors above the transistor level, between overlying levels of metal conductors.
Lead zirconate titanate (PZT) has become a prevalent ferroelectric dielectric material in FeRAM memory cells. As described in U.S. Pat. No. 6,656,748, commonly assigned herewith and incorporated hereinto by this reference, a preferred deposition technique for PZT when used as the capacitor dielectric in ferroelectric memory is metal organic chemical vapor deposition (MOCVD), especially for thin films (<100 nm). The MOCVD technique permits the film thickness to be scaled without significant degradation of switched polarization and coercive field, yielding PZT films with a low operating voltage and large polarization values. In addition, the reliability of the MOCVD PZT film has been observed to be better than that generally obtained using other deposition techniques, such as sputtering, particularly with respect to imprint/retention.
By way of further background, the integration of decoupling capacitors with PZT as the capacitor dielectric, into an integrated circuit that includes FeRAM memory cells using PZT as the ferroelectric material, is known in the art. It is known that ferroelectric materials such as PZT exhibit inherently high dielectric constants, and therefore capacitors using such materials as the capacitor dielectric provide a high capacitance per unit area. One example of such FeRAM memory integrated circuits uses sputtered PZT as the capacitor dielectric for both the ferroelectric memory cells and the decoupling capacitors.